1. Technical Field
The invention relates to a laminar flow element with an integrated turbulence filter.
2. Description of the Related Art
Such a device is described, for example, in European patent application no. 82201059.1, publication no. 0075343, corresponding to U.S. Pat. No. 4,427,030. Pressure differences and mass portions in a fluid flow channel are determined in the basis of measurements which are taken from a part of a fluid flow--the measurement flow--which is branched-off the main flow, and which flow is passed through a thin, tubular-shaped measuring channel, in which the flow is laminar. A laminar flow is defined as a flow whereby the liquid flows over itself as if it were in layers. Such a flow is stabile at flow speeds which correspond with a Reynolds number lower than 2300. The Reynolds number is the number which show the relationship in a flow between the speed of the mass and the dynamic viscosity, and which is defined as R=.rho.vd/.mu. wherein .rho. is the density of the liquid, v is the speed, d the diameter of the tube through which the flow runs and .mu. the viscosity. In order to ensure that measurements made from the measurement flow are representative for what occurs in the main flow, the main flow must also be laminar. The latter can be achieved by introducing a so-called laminar flow element into the flow. The fluid is forced to flow through the channels present in the element, which are dimensioned in such a manner that the Reynolds number is lower than 2300 and a laminar flow therefor arises. The measuring channel is installed parallel to the main flow. As long as there is a laminar flow it applies that according to Poiseuille's law the flow speed in such flow is proportional to the drop in pressure and inversely proportional to the viscosity; the ratio between the flows in the main channel and the measurement channel can now be determined.
In the aforementioned patent, a laminar flow element is described in detail. This element is constructed of piled-up plates with inflow and outflow opening(s) and with grooves, or channels therein, respectively.
In the case of a device as described in the said patent the in-going flow--i.e. the flow which is led towards the laminar flow element --is in general not laminar and turbulences occur therein. If a flow containing turbulences feeds a laminar flow element, then that is less favourable than when the ingoing flow is already entirely or mainly laminar. This expresses itself in particular in the quantity of fluid which is to be measured per minute: if turbulences are present the quantity of fluid which is to be measured per unit of time is smaller if a certain laminar flow element is used that when the ingoing flow is laminar.
One attempted solution for this problem has been in the use of a front turbulence filter, upstream from the laminar flow element. However, this proposed solution did not resolve the problem.